Synthesis, Characterization, and Testing of Catalytic Nanoparticles in a Flow Reactor (NSF CBET Funded)

Testing of Catalytic Nanoparticles

Nanosize catalytic particles are more reactive than their bulk counterparts in large part owed to their high surface-to-volume ratio. With Rowan University, platinum nanoparticles (7-9nm) were synthesized and characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM; Figures 1 and 2), and x-ray diffraction (XRD). The particles were then uniformly dispersed on a cordierite substrate and flow reactor studies were performed with different catalyst loadings using a premixture of methanol and air. The end goal is to better understand the reactivity of nanosize platinum catalysts, compare results to bulk layered catalysts, and assess the thermal stability of the catalysts subject, to repeat cycling.

What are the advantages of Catalytic Nanoparticles?

It has long been recognized that nanosized catalysts are more reactive than their bulk layered counterparts,

What limits the use of Catalytic Nanoparticles?

Loss of surface area and morphological changes owed to sintering and restructuring during use, limit the benefits of catalytic nanoparticles.

How Can Catalytic Nanoparticles be Modified to be More Useful?

If a high activity catalyst can be maintained, the amount of catalyst material needed can be reduced, shorter catalyst startup times achieved and lower temperature operation made possible.

Case Study: Catalytic Nanoparticles in a Flow Reactor

In this study, platinum nanoparticles were synthesized using wet chemistry, their reactivity assessed in a bench-scale quartz flow reactor and sintering evaluated by subjecting new samples to repeated cycling and/or controlled temperature environments.

Experimental Apparatus

Our platinum nanoparticles were synthesized using wet chemistry. Information on particle size distribution was obtained from TEM images. The catalysts were then loosely deposited on a cordierite substrate. Air was bubbled through methanol maintained in a fixed temperature bath to provide the premixed methanol-air mixture at variable flow rates with composition dependent on the vapor pressure of methanol. During the tests, the temperature of the catalyst substrate was measured and the exhaust gas composition was sampled and analyzed using gas chromatography.

Results

Interestingly, room-temperature light off was achieved (as previously noted by Hu and co-workers [1,2]) followed by temperature excursions typically on the order of 500^oC to 800^oC depending of the fuel-air composition, flowrate, and catalyst loading. For each experiment, multiple repeat tests were performed and the temperature excursions were measured. Representative temperature histories are shown in Figure 3. In addition, repeat cycles were run to evaluate sintering and restructuring of the catalysts. Images of the catalyst after repeated cycling and fresh catalysts subject to uniform temperatures for a prescribed period of time have been obtained. For more detailed information, kindly refer to reference [3].

Figure 1: Transmission Electron Microscopy (TEM) image of the Pt nanoparticles (Courtesy of Professor Bakrania, Mechanical Engineering, Rowan University).

Figure 2: Size distribution of the Platinum nanoparticles showing relatively narrow size distribution (Courtesy of Professor Bakrania, Mechanical Engineering, Rowan University).

Figure 3: Temperature histories of catalyst substrate with different methanol-air flowrates showing reproducibility of the reaction through multiple repeat cycles and increasing reaction temperature with increasing flowrate.

Figure 3: Temperature histories of catalyst substrate with different methanol-air flowrates showing the reproducibility of the reaction through multiple repeat cycles and increasing reaction temperature with increasing flowrate.

Hu, Z., Boiadjiev, V., Thundat, T., Energy and Fuels 19 (2005) 855-858.
Hu, Z., Thundat, V., Proc. of 2006 ASME Power Conf., PWR2006, May 2-4 2006 545-550.
Applegate, J., McNally, D., Pearlman, H., Bakrania, S. (2013) “Platinum Nanoparticle Combustion of a Methanol-Air Mixture,” Energy and Fuels 27(7) 4014–4020.